1. Field
The present disclosure relates to the design of an optical device. More specifically, the present disclosure relates to the design of an optical device that includes components having a common etch depth.
2. Related Art
Engineers are beginning to investigate possible designs for a multi-chip module (which is sometimes referred to as a ‘macrochip’) that integrates processor chips and memory chips to enhance system performance. In order to function properly, the macrochip is expected to require high-bandwidth, high-density, low-latency and low-power interchip and intrachip optical communication networks. A variety of optical communication network topologies have been proposed, all of which include extensive optical-waveguide routing. With large-scale integration, the optical-waveguide routing length may be as long as 100 cm for some optical links, which requires ultralow-loss (such as less than 0.1 dB/cm) optical waveguides. Furthermore, high-density optical-waveguide routing (with tightly spaced parallel optical waveguides and tight bends) in the macrochip is also advantageous.
If the optical-waveguide routing is implemented on a single photonic layer, optical-waveguide crossings will be an essential element in the optical communication networks. Although optical-waveguide crossings can potentially be made with very low optical loss (for example, approximately 0.1 dB) and low crosstalk (such as −40 dB), they typically present severe constraints to the scaling of an optical communication network because a large number of optical-waveguide crossings may be needed for routing in a single photonic layer. One way to avoid this problem is to use multilayer routing, which avoids optical-waveguide crossings at the cost of interlayer optical couplers. However, if each optical link includes less than five interlayer hops, the optical loss due to the interlayer coupling can be less than 10 dB.
Because of the high index-of-refraction contrast in silicon optical waveguides and compatibility with CMOS fabrication, silicon photonics is a promising technology that can be used to implement the optical communication networks. While silicon optical waveguides can enable very compact optical devices, and thus can help provide low-power and high-density optical links, these optical waveguides also usually significantly increase the optical scattering loss at the optical-waveguide core-cladding boundary. For example, the pass-through optical loss of a compact sub-micron silicon optical waveguide is typically around 1-2 dB (or 10-20 dB/cm). In order to reduce the optical loss, a large optical mode is usually needed. However, this approach contradicts the requirements of high-density routing and low-power active devices.
Current techniques for addressing this problem usually involve complicated fabrication processes with multi-step etching operations. While these techniques can provide low-loss optical waveguides and low-power active devices, they often do not allow high-density routing because the optical-waveguide mode size is too large. In addition, the multi-step etching operations can cause additional optical loss at transition sections in the optical communication networks, and thus may reduce the yield.
Hence, what is needed is an optical link without the above-described problems.